Why eevee renders reflective objects in black and cycles does not?
I have discovered that the problem discussed here, as well as other recent rendering posts, may be linked to a video issue related to recent updates.
After duplicating the issues on three computers, all of which meet the video requirements as stated by Blender documentation, I began trying several recent Blender versions. All exhibited rendering issues except Bv2.81.
Thanks to all who helped.